Cardiolipin (CL), a mitochondrial phospholipid initially identified in the heart, plays a pivotal role in maintaining normal cardiac function. In mammals, the biological function of CL is determined by the composition of its fatty acyl chains which is dominated by linoleic acid (18:2) in metabolic tissues, such as heart, liver, and skeletal muscle. This unique acyl composition is believed to support mitochondrial membrane proton gradient and activity of various mitochondrial enzymes and proteins. Consequently, a loss of tetralinoleoyl CL (TLCL), the predominant species in the healthy mammalian heart, occurs during the onset of heart failure both in rodents and humans with dilated cardiomyopathy. CL is biosynthesized in a series of steps from phosphatidic acid. Newly synthesized CL must go through a remodeling process that involves phospholipases and acyltransferase/transacylases to incorporate linoleic acid into its fatty acyl chains. Accordingly, defective CL remodeling causes dilated cardiomyopathy in Barth syndrome, an X-linked genetic disorder characterized by linoleic acid deficiency in CL, mitochondrial dysfunction, growth retardation, and neutropenia. Furthermore, aberrant CL acyl composition from pathological CL remodeling has been implicated in the etiology of mitochondrial dysfunction associated with a host of pathophysiological conditions in aging and age-related diseases including diabetes, obesity, cardiovascular diseases and neurodegeneration, all of which are characterized by oxidative stress, CL deficiency, enrichment of docosahexaenoic acid (DHA) in CL, and mitochondrial dysfunction.